1. Field of the Invention
The present invention relates to electric analog indicators and, more particularly, to air-core gauge devices having orthogonally wound deflection coils.
2. Description of the Prior Art
In a conventional air-core gauge with normal orthogonally positioned electro-magnetic deflection coils wound about a non-metallic material bobbin, a problem exists in producing electro-magnetic fields of equal intensity in the orthogonally positioned deflection coils. Within a central region of a cavity of the bobbin, a magnetized rotor rotatably mounts in magnetic proximity to the deflection coils and attaches to an indicator needle which moves angularly over a series of linear graduations on a dial face to indicate changing conditions.
With one coil closer to the rotor than the other, the radii are different. If both coils had an equal number of windings, the coil closest to the rotor would produce a higher field intensity than the other if energized by equivalent current signals. Hence, various strategies exist to balance the effect of the individual fields. One approach includes providing one coil with fewer windings than the other. Another requires different size wire for the windings. Such approaches have provided some assistance in promoting linearity.
Such strategies have not only increased the cost of air-core gauges, but in some instances have increased the size of the device.
Also, in gauges where more than one quadrant of the indicator dial is used and the dial pointer moves from 0.degree. to over 270.degree., i.e., when the dial graduations expand to permit reading beyond 90, 180 or even 270 degrees, a current signal reversal in both windings must occur in order for the pointer to cross over the interface between quadrants. If the size of wire of the windings or the number of the windings differ, the shape of the two individual magnetic fields will differ; hence, a sum of the two fields yields an unbalanced resultant field upon which the rotor aligns causing further inaccuracies in the instrument.
Realizing the above conditions exist, efforts were made toward devising resultant electro-magnetic fields from the deflection coil which eliminated the imbalance between the orthogonally positioned coils. That effect resulted in the present gauge device that contains structure that appears to depart from the prior art cross coil structure.